Understanding the reaction pathway of lithium borohydride-hydroxide-based multi-component systems for enhanced hydrogen storage

Abstract

Complex hydride–metal hydroxide multicomponent hydrogen storage systems have high potential for hydrogen storage because their dehydrogenation thermodynamics can be tuned while maintaining a high hydrogen storage capacity. Out of all the ratios explored using lithium borohydride and lithium hydroxide (LiBH₄–xLiOH, x = 1, 3, 4), a particularly promising system is LiBH₄–3LiOH with a maximum storage capacity of 7.47 wt%. Thermal and diffraction studies along with in situ neutron diffraction reveal new insights into the intermediate phases involved in the reaction pathway, enabling the identification of a detailed reaction schematic. The onset decomposition temperature was reduced to 220 °C for the hand-milled 1 : 3 system, releasing 6 wt% of H₂ by 370 °C. Li₃BO₃ was the main decomposition product. Other than a small trace of water, no toxic gas release was detected along with the H₂ release. Ball-milling showed improved reaction kinetics by releasing around 6 wt% between 200 and 260 °C in one step. The destabilization was achieved through the coupling reaction between H^δ− in [BH₄]⁻ and H^δ+ in [OH]⁻. Among all the catalysts investigated, the addition of 5 wt% NiCl₂ led to further improvement in reaction kinetics. This resulted in a decrease in the onset decomposition temperature to 80 °C and released 6 wt% of H₂ below 300 °C. The systems have exhibited improvements in kinetics and operational temperature, showing potential as a single use hydrogen storage material.